Mechanical possibility of hybrid propulsion conversion

[Shlomi]

This is my first post here, so hello all!
I’ve a 50 feet Boreal with NANNI DIESEL N4.100 engine.
I’m about to make a refit of the electrical system, including solar panels and a large Lithium batteries bank.
I need advice whether hybrid propulsion conversion is mechanically possible. I was thinking of using two 20kW BLDC motors, similar to Beta Marine hybrid engine setup. I think that maybe the motors could be connected to a sprocket on the engine shaft. The diesel engine will be geared in neutral when the electric engines will drive the boat.
I’m not sure that this is the only, or the best option, so I’ll appreciate any advice
Photos of the engine shaft attached.


Thanks,
Shlomi

[Muaddib1116]

Doesn't look like there's much space there to work with. I think you would need a way to disengage the electric motors while using the diesel engine. Whether that can be done at the electric motors, or if you would need to add some sort of clutch, I don't know. Based on Sailing Uma's early attempts at their DIY electric motor, a sprocket on the prop shaft with a chain to the motors is going to have a lot of noise and vibration, and it's going to load the shaft out of alignment with the diesel transmission. I'm not sure this is a good DIY project on such an expensive boat.

[Shlomi]

Good point about the chain noise.
Can't electrical motors disengaged from the controller instead of using a clutch?

[ranger58sb]

Originally Posted by Shlomi

I need advice whether hybrid propulsion conversion is mechanically possible. I was thinking of using two 20kW BLDC motors, similar to Beta Marine hybrid engine setup. I think that maybe the motors could be connected to a sprocket on the engine shaft. The diesel engine will be geared in neutral when the electric engines will drive the boat.

What problem would you be trying to solve? What would you be trying to accomplish? IOW, why? What would success look like?

-Chris

[Matt Johnson]

Beta uses a mechanical shaft decoupler - not a clutch - to disengage the prop shaft. Between the diesel and electric motors is a hydraulic gearbox capable of unlimited free wheeling. You'll need to check with the gearbox manufacturer if you can freewheel or not.

[ItDepends]

All those things CAN be done.

But, Why? Exactly? How will doing this make your boat better?

[mcarthur]

Does your gearbox allow freewheeling?

If so, and especially if it's speed-limited because you will be on electric, then you could do a permanent belt connection between a shaft-mounted pulley and one off the electric motor(s). The motors would be off to one side of the shaft, but possibly mounted to the engine so that vibrations don't effect the belt tension. Although if your shaft-to-gearbox mount is already vibration- or angle-friendly then you may be able to separately mount the motor.

Use the differential in motor pulley and shaft pulley to give you the appropriate gearing, but take into account the diesel+gearbox gearing running back up the belt to the motor for generating electricity.

I was looking into having the shaft pulley being split so that it's easy to add/remove for testing purposes.

There will be considerable (depending on your motor size) side forces from the belt on the prop shaft though: running 5kW through may be very, very different to running 30kW! I've no idea how to quantify the risk and issues though: our PTO on the other end of the engine allows 6Kw to be taken off, but that's a power issue rather than a shaft I assume (ie. it would still be there if you weren't side-loading the PTO shaft and going direct gearing).